1. Field of the Invention
The present invention relates to an X-ray diagnostic apparatus having a fluoroscopy mode for displaying an X-ray fluoroscopic image on a monitor or display, and a radiography mode for recording an X-ray radiographic image on a recording medium such as an storage phosphor or X-ray film.
2. Description of the Related Art
An X-ray diagnostic apparatus of this type comprises X-ray generator 1, spot-shot device 2, fluoroscopic image generator 3, monitor 4, and controller 5, as shown in FIG. 1. X-ray generator 1 can generate both fluoroscopic and radiographic X-rays. Spot-shot device 2 records an X-ray radiographic image on an X-ray film or storage phosphor as a recording medium. Fluoroscopic image generator 3 includes an I.I. (image intensifier) for converting an X-ray fluoroscopic image into an optical image, and a TV (television) camera for converting the optical image output from the I.I. into an analog video signal. Thus, generator 3 converts an X-ray fluoroscopic image into an optical image, and then converts the optical image into an analog video signal. Spot-shot device 2 and generator 3 oppose X-ray generator 1 to sandwich the object to be examined (the patient) P therebetween. Monitor 4 displays a fluoroscopic image based on the analog video signal supplied from generator 3. Controller 5 controls the above-mentioned sections. The X-ray diagnostic apparatus described above has two modes, i.e., fluoroscopy and radiography modes. In the fluoroscopy mode, fluoroscopic X-rays are generated from generator 1, and an X-ray fluoroscopic image based on the fluoroscopic X-rays is converted to an analog video signal by generator 3. The analog video signal is supplied to monitor 4. Therefore, the X-ray fluoroscopic image is displayed on monitor 4 as a motion image. In the radiography mode, radiographic X-rays are generated from generator 1 in synchronism with the operation of spot-shot device 2, and an X-ray radiographic image based on the radiographic X-rays is recorded on a film or storage phosphor by spot-shot device 2.
In normal diagnostic procedures, a portion to be radiographed (to be referred to as a radiography portion hereinafter) and a radiographic timing are determined while observing an X-ray fluoroscopic image displayed on monitor 4 in the fluoroscopy mode, and a radiography switch (not shown) for inputting a radiography instruction to controller 5 is then operated. When the radiography instruction is input, the radiography mode is set, and spot radiography is made on a recording medium such as an X-ray film or storage phosphor.
However, a radiography portion and a radiographic timing requested by an operator during X-ray fluoroscopic image observation do not often coincide with those of an actually radiographed X-ray image. In an X-ray image obtained in this case, at least one of a radiography portion and a radiographic timing is different from those requested by the operator. This is for the following reason. That is, after a radiography instruction for switching from the fluoroscopy mode to the radiography mode is supplied, radiography cannot be executed before a time required for conveying a recording medium used for radiography, and a time required for achieving a high-speed rotation of a rotary anode of an X-ray tube for switching a fluoroscopic X-ray to a radiographic X-ray in generator 1 have passed. For this reason, a time lag of 1 to 2 sec is generated from when the operator operates the radiography switch until the radiographic X-rays are actually radiated.
Because of the presence of the time lag, a radiography portion makes an irregular motion or the concentration of a contrast medium falls outside a desired value, thus causing a radiography failure. In a normal case, successful radiography can be determined only after the recording medium is developed or visualized by image reading. For this reason, after a considerable time has passed from the radiography, the operator finds out that radiography has been unsuccessful. When radiography fails, if contrast radiography such as an angiography is performed, a contrast medium must be injected again, thus resulting in a heavy load on a patient. In other radiography operations, an operation for performing radiography starting from the fluoroscopy mode must be performed again, resulting in cumbersome operations and a load on a patient.
In the conventional X-ray diagnostic apparatus, a radiography portion and a radiographic timing which are set by an operator while observing an X-ray fluoroscopic image displayed on a monitor in the fluoroscopy mode do not coincide with those of an X-ray radiographic image recorded on a recording medium, e.g., a storage phosphor or X-ray film due to the presence of a time lag. Thus, diagnosis data desired by an operator cannot be obtained from an X-ray image recorded in the radiography mode.